Ozone is the most damaging component of smog and results in a variety of physiological effects that may significantly impact public health in polluted urban areas. The mechanism by which ozone is formed in photochemical smog involves an alkyl peroxy radical intermediate that couples the chemistry of NO to odd oxygen formation. The goal of this project is to measure the rate coefficients for reactions of alkyl peroxy radicals with a number of trace atmospheric constituents. The project has three distinct components. First, the mid-IR spectra of alkyl peroxy radicals will be determined using a long path length absorption FTIR apparatus. Alkyl peroxy radicals will be generated by reaction of atomic chlorine with the parent alkane followed by association with molecular oxygen. Second, the IR spectra will be verified using both experimental and theoretical techniques. Experimentally, disappearance of the observed bands will be monitored followed titration of the alkyl peroxy radical with an excess of either chlorine or nitric oxide. IF frequencies and intensities will also be determined using ab initio computations. The geometry and energetics of the radical will be calculated using 2nd order Moeller-Plesset perturbation theory with a 6-31G* basis set. Frequencies and intensities are calculated from the optimized geometry of the radical. Third, the rate coefficients will be measured for reactions of alkyl radical with nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2). Kinetic measurements will be performed on a flash photolysis/pulsed CO2 laser thermal lens spectrometry apparatus in which peroxy radicals are generated by photolysis of a gas mixture including Cl2, the parent alkane, and oxygen, and the concentration of the peroxy radical is monitored using thermal lens spectroscopy. Kinetic information is acquired by varying the time delay between firing of the xeno flashlamp and Co2 laser. The rate coefficients determined in this study will ultimately be used in chemical models of urban air chemistry to determine the impact of individual hydrocarbon species on the production of ozone in smog.